Well completion refers to various operations to prepare a well for production, and may include casing, cementing, perforating, stimulating, gravel packing, hanging production tubing, and installing a christmas tree at the wellhead.
After drilling a subterranean wellbore, individual lengths of metal tubulars are typically secured together to form a production casing string that is positioned within the portion of the wellbore that traverses a pay zone. Production casing string increases the integrity of the wellbore and provides a path for producing fluids from producing intervals within the pay zone to the surface. Conventionally, the production casing string is cemented within the wellbore, initially forming a closed hole. To produce fluids into the production casing string, hydraulic openings or perforations must be formed through the casing string, the cement sheath, and a short distance into the formation.
These perforations may be created by a perforating gun. A series of shaped charges are held in a hollow steel carrier. The perforating gun is positioned within the cased wellbore by a tubing string, wireline, slick line, coiled tubing, or other conveyance. Once the perforating gun is properly positioned in the wellbore adjacent to the formation to be perforated, the shaped charges may be detonated, thereby creating perforations through the hollow steel carrier and the desired hydraulic openings through the casing and cement sheath into the formation.
Perforating operations may be performed in stages, intervaled by optional stimulating and/or gravel packing operations. Stimulating operations may include, for example, acidizing or hydraulic fracturing. Accordingly, as a perforating gun is run into a wellbore for perforating a given stage, a settable plug may also be run by the conveyance carrying the perforating gun. The plug may be set between a previously perforated, stimulated and/or packed stage and the next adjacent stage to be perforated, thereby isolating the previously completed stage to allow pressurization of the newly perforated stage for stimulation and gravel pack operations. After the plug is set, the next stage is perforated, and the perforating gun it is pulled from the wellbore. This operation of setting a plug and perforating may be colloquially referred to by routineers as “plug & perf.” Stimulation and/or gravel pack operations may then be performed for the newly perforated stage. This process of plugging, perforating, and stimulating/gravel packing may be repeated stage by stage, moving uphole as the completion process continues.